JPH02105106A - Optical fiber - Google Patents

Abstract

PURPOSE:To obtain the optical fiber having a sufficient hydrogen resistance characteristic and mechanical strength by specifying the crystal structure of a carbon film. CONSTITUTION:The carbon film 2 is provided on the bare optical fiber 1 and a resin film 3 is further provided at need on this carbon film 2. The carbon film 2 in this case refers to the carbon film which is obtd. by thermally decomposing a raw material compd. contg. carbon and with which the ratio R=I1,360/I1,600 of the intensity I1,600 of the Raman rays generated in a 1,575 to 1,600cm<-1> oscillation region and the intensity I1,360 of the Raman rays generated in a 1,355 to 1,360cm<-1> oscillation region attains 0.75 to 1.40. The crystal structure of the carbon film indicating such Raman spectra contains much amorphous part to the extent at which sufficient hydrogen permeation blocking capacity is obtd. and is soft to the extent of not damaging the surface of the bare optical fiber. The optical fiber which has the sufficient hydrogen resistance characteristic and exhibits the high mechanical strength is obtd. in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical fiber formed with a carbon film, and the hydrogen resistance and mechanical strength thereof are significantly improved by specifying the crystal structure of the carbon film. This is how it was done.

[Prior Art] When a silica-based optical fiber comes into contact with hydrogen, absorption loss due to the molecular vibration of hydrogen molecules diffused into the fiber increases, and PtOs, which is contained as a dopant, increases.
GeOt, BtOs, etc. react with hydrogen and
Since it is incorporated into the fiber glass as an i group, OH
There is a problem in that transmission loss due to absorption of the radical increases.

In order to deal with such adverse effects, a method of filling an optical cable with a liquid composition having hydrogen absorption ability (Japanese Patent Application No. 1983) was proposed.
-251808), but the effect is not sufficient and the structure is complicated, resulting in economical problems.

In order to solve these problems, chemical vapor deposition method (
It has been announced that a carbon film is formed on the surface of the tip fiber by a CVD method (hereinafter abbreviated as CVD method), thereby improving the hydrogen resistance of the optical fiber.

[Problem to be solved by the invention] However, in order to improve the hydrogen resistance of a carbon film, it is necessary to increase the amorphous portion with a dense structure.
Carbon coatings with many amorphous parts are hard and damage the optical fiber surface during formation, reducing the mechanical strength of the optical fiber. I haven't been able to get it yet.

This invention was made to solve the above problems, and aims to provide an optical fiber having sufficient hydrogen resistance and mechanical strength by specifying the crystal structure of the carbon coating.

[Means for Solving the Problems] The optical fiber of the present invention has a length of 1575 to 1600 cm-'
The intensity of Raman rays generated in the frequency region of ■1゜oo,
The ratio of the intensity of the Raman line generated in the frequency range of 1355 to 1360 co+-' to 1.13IO is R= I t3s.

The solution was to have a carbon film with /1+soo of 0.75 to 1.40.

[Function] The crystal structure of the carbon film exhibiting such a Raman spectrum has a large enough amorphous portion to provide sufficient hydrogen permeation blocking ability, and is soft enough not to damage the surface of the bare optical fiber. , it has both hydrogen resistance and mechanical strength, making it suitable for practical use.

The present invention will be explained in detail below.

FIG. 1 shows an example of the optical fiber of the present invention, and reference numeral 1 in the figure indicates a bare optical fiber. The bare optical fiber 1 is made of glass such as quartz glass or multi-component glass. A carbon coating 2 is placed on the bare optical fiber 1.
is provided.

A resin corrugated film 3 is further provided on this carbon film 2 as required.

The carbon film 2 here is obtained by thermally decomposing a raw material compound containing carbon! 575-1600cm
Intensity of Raman line generated in the frequency region of -' 1 +ao
o and the intensity of Raman rays generated in the frequency region of 1355 to 1360 cm-'■1.6°Ratio R-I 136G
/111800 is 0.75 to 1.40.

The hydrocarbon used as a raw material compound for the carbon film 2 is not particularly limited as long as it can deposit a carbon film by thermal decomposition, but from the viewpoint of the properties and precipitation rate of the carbon film 2 that is formed, Hydrocarbons or halogenated hydrocarbons with carbon numbers of 15 or less are desirable, and in particular chlorinated aliphatic hydrocarbons with carbon numbers of 2 have a fast carbon film deposition rate, so the time required to obtain a predetermined film thickness should be shortened. This is suitable because it allows for If the number of carbon atoms is 16 or more, the rate of decomposition of the raw material compound into carbon becomes extremely slow, which is not preferable. Further, as the halogen atom to be substituted for the hydrogen atom of the hydrocarbon, chlorine is preferably used from the viewpoint of handling such as toxicity. In addition, carbon compounds with oxygen atoms in their structures, such as alcohols, ketones, and esters, have very low efficiency of carbonization through decomposition and tend to generate soot-like substances, so they cannot be used at present. .

Furthermore, the thermal decomposition temperature of the raw material compound is not particularly limited;
00°C to too0°C is suitable. If the temperature is below 400°C, thermal decomposition of the raw material compound will not occur, and the annealing point of quartz will be 11
70℃, and if the temperature exceeds this temperature, the crystal structure of the tip fiber changes and becomes brittle, so it cannot be heated above ttoo℃.The method for decomposing the raw material compound is a resistance heating furnace, induction heating. Thermal decomposition methods such as furnaces and infrared heating furnaces, or after vaporizing the raw material compound into a gaseous state, diluting it with an inert gas such as nitrogen, helium, or argon, and generating plasma using high frequency or microwaves. , ion decomposition method, etc. can be used.

Figure 2 shows the optical fiber of this invention with 1000~! 800c
This shows a Raman spectrum in the ++-' frequency region. The peak centered at 1600ca+-' is due to the two-dimensional hexagonal lattice forming each layer of the graphite structure of carbon, and the larger this peak, the higher the crystallinity of the carbon film. Also 1 360cm-'
The peak centered around ° is caused by the decrease in the symmetry of the two-dimensional hexagonal lattice due to structural defects in the graphite structure, or the disappearance of the hexagonal lattice structure. There will be many.

By the way, if the carbon film 2 has a high degree of crystallinity, the six-membered ring structure will be regularly arranged, making it soft. The shrinkage that occurs during the formation of the carbon coating 2 can be alleviated, and the internal strain of the bare optical fiber l can be absorbed, as well as the stress applied to the optical fiber from the outside. Be able to improve your objective strength. On the other hand, a carbon film with many amorphous parts is harder than a highly crystalline carbon film and may damage the surface of the bare optical fiber 1 during formation, but its dense structure allows for very high hydrogen permeability. Demonstrates deterrent ability. Therefore, 1600ca+- indicating the crystallinity of the carbon coating 2
1360 cm-' showing the peak and amorphous part of '
By finding the ratio R=I +eoo/I +*eo of the intensity of each peak of 118oo and 1+360 and keeping this constant, it is possible to obtain a carbon film 2 that has both mechanical strength and hydrogen permeation blocking ability. Can be done. 1600c
Intensity ratio R of the peak at m-' and the peak at 1360 cm-'
To find the carbon coating 2 on the surface of the bare optical fiber 1, first
After forming, the Raman spectrophotometer measures I 000~
A Raman spectrum in the frequency region of I 800 cm-' is obtained. A normal laser Raman spectrophotometer can be used as this Raman spectrophotometer. Next 1575-160
0cm-'' frequency range and 1355-1360cn-'
Find the peaks in each frequency region. For the strong side of the peak, draw the baseline as shown in Figure 2, measure the height from the baseline, and take this height as the respective intensity 111100q I +3110, R = 113
110/I +so.

seek.

A test example for determining the appropriate value of R will be described below.

[Test example] Bare optical fiber to find the appropriate value of the intensity ratio R! A carbon film 2 was formed on the surface under various conditions, and the Raman spectrum and characteristics such as mechanical strength and transmission loss of the obtained optical fiber were evaluated.

(Test Example 1) A resistance heating furnace through which a quartz tube with an inner diameter of 40 mm was passed was installed in a spinning device for spinning bare optical fiber from an optical fiber base material. Next, an optical fiber base material having an outer diameter of 30 mm and having a core impregnated with GeO7 as a dopant was placed in this spinning apparatus. The fiber preform is then heated to 2000°C and spun into an optical fiber with an outer diameter of 125 μm at a spinning speed of 30 m/min.
While heating to ℃, benzene vapor diluted with argon gas to about 5v01% as a raw material compound for forming a carbon film was supplied at a flow rate of about 5ff/min to form a carbon film on the surface of the spun optical fiber. .

(Test Example 2) An optical fiber was manufactured in exactly the same manner as in Test Example 1 except that the temperature in the resistance heating furnace for forming the carbon coating 2 was set to 950°C.

(Test Example 3) An optical fiber was manufactured in exactly the same manner as in Test Example 1 except that 1.2 dichloroethylene was used as the raw material compound and the temperature in the resistance heating furnace was 650°C.

(Test Example 4) An optical fiber was manufactured in exactly the same manner as Test Example 1 except that 1.2 dichloroethylene was used as the raw material compound and the temperature in the resistance heating furnace was 2500°C.

(Comparative Example 1) An optical fiber base material having an outer diameter of 30 mm and having a core impregnated with Gemt as a doping agent was installed in a spinning device that spins bare optical fiber from an optical fiber base material, and this was
Heated to 000°C and spun at a spinning speed of 30 cm/min to create an outer diameter of 12 mm.
It was spun into a 5 μm optical fiber.

The Raman spectra of each of the optical fibers of Test Examples 1 to 4 thus obtained were measured in the frequency range of 1000 to 1800 cm-' using a laser Raman spectrophotometer. This laser Raman spectroscopy requires 488 yen as a light source.
An RV argon laser is used, a holographic diffraction grating with an effective wavelength range of 450 to 850n111 and 1800 lines/m+e is used as the diffraction grating, the Raman light focusing optical system is 50mm+, and a total reflection prism is used as the laser beam introduction element. The measurement was carried out with a frequency accuracy of ±1 cm-'.As a result, there were large vibrations caused by carbon in the frequency region of 1355 to 1360 cm-' and the frequency region of 1575 to 1600 cm-'. Peaks were observed.Next, the intensity of these peaks taoo, I +38
G is measured respectively, and from this the intensity ratio R=I 13g
. /[,6°. I got it. A graph illustrating these Raman spectra and the value of the intensity ratio R are shown in FIG. For comparison, FIG. 3 also shows a graph illustrating the Raman spectrum of natural graphite.

In addition, the median fiber strength, fatigue test at room temperature and pressure,
The increase in transmission loss at a wavelength of 124 μm was examined before and after leaving it in a hydrogen atmosphere at 80° C. and 1 atm for 24 hours, and the hydrogen resistance and mechanical strength of the obtained optical fiber were examined.

The results are shown in Table 1 along with the strength ratio R.

(Hereinafter, blank space) From the results in Table 1, it was found that the optical fibers having both hydrogen resistance and mechanical strength were Test Examples 2 and 3. Raman line intensity in several regions 1 taoo and 1355 to 1360 cm-
The intensity of the Raman line in the frequency region of '! Ratio to +3110 UL = 11380/ I taoo's appropriate value is 0
It was found that the temperature was 75 to 1.40.

[Example] A resistance heating furnace through which a quartz tube having an inner diameter of 4011 IM was passed was installed in a spinning device for spinning bare optical fiber from an optical fiber base material. Next, an optical fiber base material having an outer diameter of 30II1 m and having a core impregnated with Ge0 as a doping agent was placed in this spinning apparatus. This optical fiber base material
Heated to 0℃ and spun at a spinning speed of 30m/min to an outer diameter of 125μ.
At the same time as spinning into an optical fiber of m, t taoo and 11
Trichloroethane diluted with argon gas to about 5 vol. 1% as a raw material compound for forming the carbon film was heated in the resistance heating furnace to 1100° C. so that the intensity ratio R to 111° was in the range of 075 to 1.40. Steam about 5 (2/
A carbon film was formed on the surface of the bare optical fiber that was spun by supplying the fiber at a flow rate of 100 min. When the Raman spectrum of this optical fiber was examined and the value of the intensity ratio R was determined, it was found that R=0.84, which was confirmed to be an appropriate value. The strength of this optical fiber is 5.3 kg, the fatigue index is 200.80°C, and it is 1.24 μm before and after being left in a hydrogen atmosphere of 1 atm for 24 hours.
No increase in transmission loss was observed at any wavelength, and it was confirmed that the material has both mechanical strength and hydrogen resistance and is suitable for practical use.

[Effects of the Invention] As explained above, the optical fiber of the present invention has 157
The ratio R- of the intensity of Raman rays generated in the frequency range of 5 to 1600 cm-' (summer+soo) and the intensity of Raman lines generated in the frequency range of 1355 to 1360 cm, 1136G.
Since it has a carbon film of 1+3@O/1 +soo/J'0.75 to 1.40, there are moderate amounts of dense amorphous parts and soft crystal parts that exhibit hydrogen permeation blocking ability. Therefore, it has sufficient hydrogen resistance properties and exhibits high mechanical strength.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view showing an example of the optical fiber of the present invention, Fig. 2 is a graph showing the Raman spectrum of the optical fiber of the invention, and Fig. 3 is an optical fiber with a carbon coating formed under various conditions. This is a graph schematically showing the Raman spectrum of . ■...Optical fiber bare wire, 2...Carbon coating.

Claims (1)

[Claims] Intensity I_1_6_0_0 of Raman rays generated in the frequency range of 1575 to 1600 cm^-^1 and 1355 to 1
Ratio of intensity I_1_3_8_0 of Raman rays generated in the frequency region of 360 cm^-^1 R = I_1_3_6_0
Optical fiber having a carbon coating with /I_1_6_0_0 of 0.75 to 1.40